Primitive Spiders

Infraorder Mygalomorphae

Primitive spiders (Mygalomorphae) are amongst the largest and certainly the longest lived spiders. These are the least evolved spiders known from Australia and one of the oldest groups in the fossil record. They have remained almost unchanged for tens of millions of years.

Primitive spiders are heavily built, often quite slow moving and have features reminding us of their burrow-dwelling life style.

They have fangs that bite down (like snakes) and 2 pairs of lungs (under their body).

Unlike the modern orb-weavers, for example, most Mygalomorphae have only four spinnerets (often quite hidden at the end of the abdomen) and a few species have only two. After all, they only need silk mostly for lining the burrow and making the egg sac.

Generally, identification of mygalomorph spiders to family requires good knowledge and often a microscope but is usually possible from good photographs. However, recognition of species and often of genus, especially if we don’t know where it comes from, is very difficult for scientists without the animal. Often, spiders belonging to families that have been recently studied intensively in Australia are the most accurately identified.

Males are generally easier to identify than females. This is especially so with Funnelwebs but not so for tarantulas.

Mygalomorphae live for many years (15–25) and most are not adult until 5–7 years old.

Golden Trapdoor egg sac suspended in a burrow.

Female mygalomorphs live for up to 25 years. Each year they shed their outer skin (moult) and mate.

Males look and behave like females until they become adult. Once mature, the male spider has a relatively short life (maximally 3–6 months). His purpose is simply to find a female and mate and he transforms into a lanky-legged, scrawny animal designed for actively searching for the female. Guided partly by the air-borne scent (pheromone) of the female, he wanders at night, searching. Once the male finds a female mating takes place at the burrow entrance.

In a few days (up to a week), the female makes the egg sac into which she places the eggs. As she drops the eggs, they are made fertile. The egg sac is usually suspended like a pillow in the bottom of the burrow. Humidity and temperature may be partly controlled by a thin film of silk she places just below the top of the burrow.

After several weeks, the spiderlings have moulted once in the egg sac. They are now dark in colour. They chew a hole in the egg sac and emerge to live with the mother. They remain with her for sometime, living partly from their yolk but also feeding at the mouth of the mother when she feeds.

Females remain in their burrows and hunt at night from the burrow entrance.

Sometimes, twigs connected by silk to the entrance signal that an insect is passing by whereupon the spider launches itself out, seizes the insect and retreats to its burrow. If the burrow has a door, the spider closes it behind it.

The spider then moves to the bottom of the burrow where it crushes the prey, predigests and sucks out the contents, eventually making a packet of the broken remains which it silks into the burrow wall.

Because of their large size and stable burrows, mygalomorphs form an important food reserve for large lizards, insectivorous mammals (e.g., bandicoots and bilby) and some birds.